tr: unexpected stderr diff when head truncates pipeline

[matt-dz]

Summary

tr produced an unexpected rshell/oracle stderr diff candidate during agentic QA. When a downstream head truncates the pipeline, rshell reports broken-pipe write errors from tr; the oracle exits successfully with matching stdout and no stderr.

Run Context

• QA run id: run-20260518T233741Z-tr
• Target builtin: tr
• Scenario(s): 50 generated KIND scenarios (names omitted from this public body)
• Rshell commit/version: unknown
• Artifact reference: representative invocation inv-20260518T234915.836852464Z-e8e540e3

Command

cat /var/log/containers/* 2>/dev/null | tr -d '
' | tr -s ' ' | head -n 160

Observed Difference

• Differing dimension: stderr
• Rshell exit code: 0
• Oracle exit code: 0
• Rshell stdout summary: stdout matched the oracle output
• Oracle stdout summary: stdout matched the rshell output
• Rshell stderr summary: emitted two tr: write error: write |1: broken pipe lines
• Oracle stderr summary: empty stderr

Notes

This is an unexpected diff candidate from the QA harness. Full local artifacts are retained in the QA workspace. Maintainer judgment is still needed to decide whether rshell should suppress expected broken-pipe write errors for tr, document an intentional divergence, or adjust the harness/oracle comparison.